主蒸汽三通对流传热、热应力及寿命的计算分析

发布时间：2018-12-20 08:54

【摘要】：蒸汽管道是电厂的重要组成部分,而三通应力比较复杂,是主蒸汽管道和再热蒸汽管道强度分析的主要元件,需要给予特殊关注。由于三通几何结构的复杂性,当三通内流体发生瞬态流动时,三通的主管与支管交贯处附近形成分离区,管道横截面上产生的二次流导致三通内流体的速度场、压力场发生变化,三通交贯处附近的对流传热系数亦会显著变化。当研究主蒸汽三通热应力以及寿命时,工程实践中通常是依据圆形直管传热关联式得到的三通主管与支管平均对流传热系数常数作为边界条件,继而对三通进行热应力和寿命分析。那么,三通几何结构复杂性产生的沿程分布不均的对流传热系数与工程实践中常常采用的恒定对流传热系数相比,两种边界条件对三通热应力和寿命的计算有何差距,需要详细分析和验证。本文依托于“基于典型失效模式的超(超)临界电站锅炉事故预防关键技术研究”课题,对三通的传热特性、热应力和寿命进行了分析。本文以某电站300MW机组为范例,通过确定三通考核点在锅炉启停过程中的内压应力与热应力的合成应力强度随时间变化曲线,得到三通考核点在锅炉启停过程中的谷值时刻和峰值时刻;采用FLUENT流体软件,对谷值时刻和峰值时刻的流体与三通的共轭传热进行数值模拟,探讨三通内流体与壁面的对流传热系数的沿程变化规律;采用ANSYS有限元软件,分别以FLUENT数值模拟得到的沿程变化对流传热系数作为三通内壁面施加条件以及以圆形直管强制对流传热关联式得到的三通主管与支管的恒定平均对流传热系数作为三通内壁面施加条件,得到峰值工况与谷值工况的热应力;分别采用ASME疲劳寿命计算方法和疲劳-蠕变交合作用下的寿命计算方法,对两种壁面传热边界条件下的三通进行寿命计算和对比,研究三通复杂的几何结构导致的沿程对流传热系数分布不均,对三通热应力以及寿命的计算结果是否存在差异,以及它们的差异程度如何,从而为以后工程中对三通热应力以及寿命计算的进一步修正和完善提供合理的依据。
[Abstract]:Steam pipeline is an important part of power plant, and the three-way stress is complex, which is the main component of strength analysis of main steam pipeline and reheat steam pipeline, which needs special attention. Because of the complexity of the geometry structure of the three-way, when the transient flow occurs in the three-way, a separation zone is formed near the intersection between the supervisor of the three-way and the branch pipe, and the secondary flow on the cross section of the pipeline leads to the velocity field of the fluid in the three-way. When the pressure field changes, the convection heat transfer coefficient near the junction of the three links will also change significantly. When studying the thermal stress and life of the main steam three-way connection, the average convection heat transfer coefficient constant of the three-way pipe and the branch pipe is usually used as the boundary condition in engineering practice according to the heat transfer correlation formula of the circular straight pipe. Then the thermal stress and life of the three links are analyzed. So, compared with the constant convection heat transfer coefficient which is often used in engineering practice, the difference between the two boundary conditions and the calculation of thermal stress and life of the three-way connection is different from the convection heat transfer coefficient with uneven distribution along the path caused by the complexity of the geometry structure of the three-way connection. Need detailed analysis and validation. In this paper, the heat transfer characteristics, thermal stress and service life of three links are analyzed on the basis of "study on the key Technology of accident Prevention of Super-critical Boiler based on typical failure Mode". Taking the 300MW unit of a power station as an example, the variation curve of internal pressure stress and thermal stress intensity with time is determined by determining the internal pressure stress and thermal stress of the three-way test point in the process of boiler starting and stopping. The valley value and peak value of the three-way check point in the process of boiler start and stop are obtained. By using FLUENT software, the conjugate heat transfer between the fluid and the three-way is simulated at the valley time and the peak time, and the variation law of the convection heat transfer coefficient between the fluid and the wall in the three-way is discussed. Using ANSYS finite element software, The constant average convection heat transfer coefficient obtained by FLUENT numerical simulation is used as the condition of applying convection heat transfer coefficient along the inner wall of the three way and the constant average convection heat transfer coefficient between the tube and branch tube is obtained by the correlation of forced convection heat transfer in circular straight tube. Imposing conditions on the inner wall of the three links, The thermal stress of peak and valley conditions is obtained. The ASME fatigue life calculation method and the fatigue creep interaction method are used to calculate and compare the life of the three links under two wall heat transfer boundary conditions. This paper studies the uneven distribution of the convection heat transfer coefficient along the path caused by the complicated geometry structure of the three links, whether there are differences in the calculation results of the thermal stress and lifetime of the three links, and the degree of their differences. It provides a reasonable basis for the further modification and perfection of the thermal stress and life calculation of the three-way connection in the future engineering.
【学位授予单位】：上海发电设备成套设计研究院
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TM621.72;TK124

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